Generally, this invention relates to controlling power in electronic equipment and, more specifically, to maximizing the use of a battery""s energy in a portable electronic device.
Traditionally, power control apparatus have been developed to control power provided by a battery to a portable electronic device. These power control apparatus monitor the voltage of the battery and compare the battery voltage to a hardware undervoltage threshold. If the battery voltage falls below the undervoltage threshold, then the power to the portable electronic device is powered-off. Typically, this threshold is positioned 200-300 millivolts above the lowest operating voltage of the portable electronic device. In radio communication devices, the threshold was typically positioned 200-300 millivolts above the operating voltage of voltage regulators in the radio communication device. The voltage regulators are used to provide a steady reference to the rest of the radio communication device. By providing such a threshold, the radio communication device""s operation was very reliable, however, some unused energy remained in the battery. The amount of the unused energy differed depending upon the type of battery attached to the radio communication device.
FIG. 1 is an illustration of a voltage/drain characteristic 100 of a NiCd (nickel cadmium) battery. As can be seen from the voltage/drain characteristic, the amount of unused energy remaining in the battery after reaching the traditional undervoltage threshold 101 is minimal. FIG. 2 is an illustration of a voltage/drain characteristic 200 of a lithium ion battery. As can be seen from FIG. 2, the lithium ion battery has a linear voltage/drain characteristic. Consequently, a significant portion of unused energy remains in the battery after reaching the traditional undervoltage threshold 201. If a lower undervoltage threshold could be provided, such as threshold 203, then the operating time of the battery powered equipment would be significantly increased.
In the portable electronic device market there is a push by the manufacturers to provide long lasting operation. This is particularly true in the radio communication device market. The introduction of lithium ion batteries is a significant advance in battery technology, offering increased operation time of portable electronic devices. However, the impact of this advance is not fully exploited with a traditional power control apparatus, as described above. The traditional power control apparatus powers-off the portable electronic device even though there is a significant portion of unused energy remaining in the battery. Thus, it would be advantageous to provide a power control apparatus to utilize a larger portion of the energy in a battery before powering-off.